WASHINGTON – New government estimates of the number of Americans who become infected with the AIDS virus each year are 50 percent higher than previously believed, sources said Friday.

For more than a decade, epidemiologists at the Centers for Disease Control and Prevention have pegged the number of new HIV infections each year at 40,000. They now believe it is between 55,000 and 60,000.

The higher estimate is the product of a new method of testing blood samples that can identify those who were infected within the previous five months. With a way to distinguish recent infections from long-standing ones, epidemiologists can estimate how many new infections are appearing nationwide.

The higher estimate is based on data from 19 states and large cities that have been extrapolated to the nation as a whole.

The CDC has not announced the new estimate, but two people in direct contact with the scientists preparing it confirmed it Friday.

What is uncertain is whether the American HIV epidemic is growing or is larger than anyone thought. It will take two years of using the more accurate method to spot a trend and answer that question.

“The likelihood is that this bigger number represents a clearer picture of what has been there for the past few years. But we won’t know for sure for a while,” said Walt Senterfitt, an epidemiologist and chairman of the Community HIV/AIDS Mobilization Project, a New York-based activist group.

There is evidence, however, that at least some of the higher number may reflect an uptick in infections in recent years. Information from 33 states with the most precise form of reporting showed a 13 percent increase in HIV infections in homosexual men from 2001 to 2005.

Ironically, the news comes less than two weeks after UNAIDS, the United Nations agency responsible for charting the course of the global epidemic, drastically reduced its estimate of the number of people living with the disease worldwide. The reason was the same – crude methods of counting were replaced by better ones.

A paper describing the new U.S. estimate is under review at a scientific journal, Thomas Skinner, a CDC spokesman, said Friday night.

“We have to wait until this paper comes out, until it has gone through peer review, before we know what the new estimates look like,” he said.

Rumors have circulated for weeks in newsletters and blogs that CDC, the federal government’s principal epidemiology agency, was preparing a dramatic upward revision of HIV incidence. The Washington Blade, a gay-oriented newspaper, reported rumors of the new estimates two weeks ago.

The CDC has reported the figure of 40,000 new infections each year for more than a decade, citing it as evidence that the epidemic in this country is stable. But while widely cited, that number has never been adequately explained or justified, in the eyes of many epidemiologists.

Few doubt, however, that accurately counting new HIV infections is unusually hard. About one-quarter of people infected with the virus do not know they are. The infection is largely “silent” for a decade in most people, and a substantial number go for testing only as they develop the symptoms of AIDS, the late stage of the illness.

Only recently has CDC put intense pressure on state and city health departments to report by name everyone who tests positive for HIV. Previously, health departments only had to report people who had progressed to AIDS.

Counting only AIDS cases was an acceptable substitute for counting new infections in the era when AIDS treatment did not significantly prolong life. But with the arrival of combinations of potent antiretroviral drugs in 1995, AIDS patients began living years longer, making the estimates increasingly less accurate.

The new system in which health departments record individuals who have just tested positive for the first time will eventually provide a much clearer picture of the epidemic. However, some people oppose it, arguing that it will keep the potentially infected from coming in to be tested.

“There are so many barriers to testing and reporting,” said Mark Harrington, executive director of Treatment Action Group, an AIDS activist think tank in New York. “We are grasping in the dark, as far as I am concerned, about the real size and shape of the epidemic.”

The 19 states and cities that contributed the data for the new estimate include New York City, New York, New Jersey, Connecticut, Texas, Florida, and several Southern and Midwestern states.

AP-NY-11-30-07 2150EST

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